The influence of the concentrations of intracellular thiols on the cellular response to various radiobiological treatments will be studied employing primarily flow cytometry and cell sorting. We have developed highly specific flow cytometric and viable cell sorting assays for intracellular glutathione, and will further our development of a flow cytometric assay for NAD(P)H content. We will use these methodologies to directly measure the relationship between intracellular thiol/NAD(P)H content and cell survival (and other end points when appropriate) following treatment with (a) x-irradiation under aerobic or hypoxic conditions (b) misonidazole and other radiosensitizers (c) hyperthermia (d) chemotherapeutic drugs such as alkylating agents, nitrosoureas, methotrexate and the quinone antibiotics. Additionally, we will continue our work in isolating stable variants of reduced or enhanced intracellular thiol or NAD(P)H content by repetitive cell sorting. These clones will be tested for various responses to the treatments discussed. It is hoped that the research will lead to new approaches which may enhance the clinical efficacy of x-irradiation, heat and chemotherapeutic agents.